The present invention relates to methods for placing treatment chemicals into a portion of a subterranean formation. More particularly the present invention relates to methods of using tacky polymers to transport treatment chemicals to a portion of a subterranean formation.
Subterranean operations often use particulates coated with tackifying agents or resins. One example of a production stimulation operation using coated particulates is hydraulic fracturing, wherein a formation is treated to increase its permeability by hydraulically fracturing the formation to create or enhance one or more cracks or “fractures.” In most cases, a hydraulic fracturing treatment involves pumping a proppant-free, viscous fluid (known as a pad fluid) into a subterranean formation faster than the fluid can escape into the formation so that the pressure in the formation rises and the formation breaks, creating an artificial fracture or enlarging a natural fracture. Then a proppant is generally added to the fluid to form a slurry that is pumped into the fracture to prevent the fracture from closing when the pumping pressure is released. A portion of the proppant may be coated with a tackifying agent, among other things, to control fines from migrating into the proppant pack. A portion of the proppant may also be coated with curable resin so that, once cured, the placed proppant forms a consolidated mass and prevents the proppant from flowing back during production of the well.
An example of a well completion operation using a treating fluid containing coated particulates is gravel packing. Gravel packing treatments are used, among other things, to reduce the migration of unconsolidated formation particulates into the well bore. In gravel packing operations, particles known in the art as gravel are carried to a well bore by a treatment fluid. That is, the particulates are suspended in a treatment fluid, which may be viscosified, and the treatment fluid is pumped into a well bore in which the gravel pack is to be placed. The treatment fluid leaks off into the subterranean zone and/or is returned to the surface while the particulates are left in the zone. The resultant gravel pack acts as a filter to separate formation sands from produced fluids while permitting the produced fluids to flow into the well bore. A portion of the gravel may be coated with resin or tackifying agent, among other things, to further help control the migration of formation fines. Typically, gravel pack operations involve placing a gravel pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel designed to prevent the passage of formation sands through the pack. The gravel pack screen is generally a type of filter assembly used to support and retain the gravel placed during the gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of a particular well bore, the production fluid, and the subterranean formation sands. When installing the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a viscosified carrier fluid. Once the gravel is placed in the well bore, the viscosity of the carrier fluid is reduced, and it is returned to the surface. Such gravel packs may be used to stabilize the formation while causing minimal impairment to well productivity. The gravel, among other things, acts to prevent formation sands from occluding the screen or migrating with the produced fluids, and the screen, among other things, acts to prevent the gravel from entering the well bore.
In some situations the processes of hydraulic fracturing and gravel packing are combined into a single treatment to provide stimulated production and an annular gravel pack to reduce formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are completed with a gravel pack screen assembly in place, and the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In such a situation, the hydraulic fracturing treatment usually ends in a screen out condition creating an annular gravel pack between the screen and casing. This allows both the hydraulic fracturing treatment and gravel pack to be placed in a single operation.
In subterranean operations, a variety of treatment chemicals may be used to facilitate the production of fluids such as water and hydrocarbons. These include gel breakers, dispersing agents, and defoamers, among others. One of the challenges faced when using such treatment chemicals is placing them where they will be most effective to avoid over-use, waste, and/or potentially deleterious effects brought about by an incorrect placement. By way of example, a solid treatment chemical may be used in combination with a fracturing operation wherein proppant particulates are being placed into the formation. In that instance, if the solid treatment chemical is an agent meant to help remove a filter cake, it will be desirable for the treatment chemical to be placed not only abutting the filter cake but also as uniformly as possible. However, in such solid treatment chemicals are often of a differing size, shape, or density to the proppant particulates being placed and so they have a tendency, while suspended in the fracturing fluid, to segregate away from the proppant particulates. Such segregation often leads to non-uniform placement that, in this example, could cause incomplete removal of the filter cake. Thus, it is desirable to be able to place treatment chemicals more reliably within a portion of a subterranean formation.
In addition to coating particulates with a resin or tackifier, in some subterranean operations it may be desirable to coat other solid substrates (such as gravel packing screens and well bore tools). For example, in some gravel packing operations it may be beneficial to place a treatment chemical directly onto the screen. Moreover, many subterranean operations use various tools that may themselves benefit from being coated with a treatment chemical. Unfortunately, many treatment chemicals, particularly solid treatment chemicals are not able to be easily placed onto such solid substrates. While tacky substances such as aqueous tackifiers, non-aqueous tackifiers, and resins have been used to attach solid treatment chemicals to solid substrates such as proppant particulates, many operations and substrates would suffer negative effects from being in contact with such a relatively permanently tacky substance. Thus, it would be of great benefit to be able to place treatment chemicals onto solid substrates with a tacky substance that would substantially degrade once down hole.